Napoleon's plan at Waterloo was fairly standard in terms of the tactics of the day: an extended artillery bombardment, followed by cavalry attacks to force the enemy into square and then further attack by artillery and musket to reap the benefit of the dense formation. Infantry would always advance under the cover of artillery and/or skirmishers so as to avoid falling under too much fire themselves. It has been shown that this plan was not properly executed with the result that the various attacks were conducted separately and did not benefit from the results of each other.
A square was formed basically as a hollow column with bayonets facing out on all four sides
A decisive tactic used in the battle was to form the infantry into squares to receive a cavalry charge. A square was formed basically as a hollow column with bayonets facing out on all four sides. No horse would dare to charge into such a formation and although receiving a cavalry charge would doubtless still have been a daunting prospect, the events at Waterloo showed that infantry in square were generally fairly safe. However, infantry in square presented an ideal, densely packed target for heavy cannon and musket fire. A game of cat and mouse would develop whereby cavalry would attack to force the enemy into square and then quickly withdraw to let the artillery pound away at the concentrated target. For their part, the defending troops would have to quickly reform into line so as to reduce the danger of cannon fire. At Waterloo, the role of the attacking force was played spectacularly badly by the French under Ney while the Allied line under the guidance of Wellington played the defensive role superbly. The French heavy cavalry attacked and forced the Allied infantry into squares but did not withdraw. Instead, they milled around the squares, shielding them from the French guns and sustaining heavy casualties from musket fire into the bargain.